1. Field of the Invention
The invention relates to a method and apparatus for making a self-inflatable air mattress or cushion having an adjustable firmness characteristic and the product formed thereby.
2. Description of Related Art
The prior art literature describes several early efforts to make self-inflatable mattresses and the like. For example, U.S. Pat. No. 3,935,690 entitled "Method of Packaging and Unpackaging a Self-Inflating Air Mattress" describes a mattress which can be used for camping and which includes an open cell foam core covered with a air impervious material having a fabric exterior. Such mattresses are satisfactory for certain camping purposes but such mattresses tend to be thin and the edge of such mattresses tend not to be physically attached to the exterior covering material.
U.S. Pat. No. 3,675,377 describes another typical inflatable structure including a flexible foam core portion and a fabric covering.
The problem with structures such as described in U.S. Pat. Nos. 3,675,377 and 3,935,690 is that the exterior material is not bonded to the entire surface of the foam core but, rather, acts like a bag so that when the structure is inflated the sides or edges tend to round out. Accordingly, it is virtually impossible to form a self-inflatable mattress, using prior art techniques, which includes concavities or compound three- dimensional shapes.
FIG. 1A illustrates, in cross-sectional detail, a typical prior art self-inflatable mattress having a core and a covering. Because the coverings tend to be fabric, it is not possible to make a lap seam without losing air as shown in FIGS. 1B and 1C.
If the fabric illustrated in FIGS. 1B and 1C is sealed on only one side, then air tends to escape in the manner indicated. FIG. 1B illustrates a prior art "fin" seam and FIG. 1C illustrates a prior art "overlap" seam. It is also possible to make an overlap seam, such as illustrated in FIG. 1C, using fabric that is coated on both sides with a cement material between the two layers. Such prior art structures have several major disadvantages. First, and foremost, fabric covers, whether or not wholly or partially sealed on both sides, wrinkle when they turn corners and/or are compressed. Therefore, they cannot adequately conform to irregular shapes and tend to leak. Second, it is not possible to form a satisfactory thermoplastic welded seal between two overlapping layers of single sided coated cloth material, such as illustrated in FIG. 1C. Third, and last, the prior art techniques such as illustrated in FIGS. 1A-1C usually require adhesives or chemicals which are environmentally hazardous.
Other inflatable mattresses or structures are unknown in the prior art. See, for example, U.S. Pat. No. 1,970,803 which describes a method of making an inflatable rubber structure, such as a bed mattress. U.S. Pat. No. 4,991,244 describes an air mattress that includes a means for controlling the density and the relative firmness thereof depending upon the side of the mattress being occupied. Similarly, note U.S. Pat. No. 4,908,895.
Lastly, U.S. Pat. No. 4,167,432 entitled "Process of Making a Water Bed Mattress" describes a technique for forming a bag-like structure that can accept water and act as a suitable bed mattress.
FIG. 1D illustrates a sheet of commercially available dual melt film including a top surface S1 having a melt temperature T1 and a bottom surface S2 having a melt temperature T2 which is lower than the melt temperature T1 on the top surface S1. Acceptable films are formed from polyether polyurethane. Such films are generally used for purposes other than making self-inflating air mattresses or cushions.
While the prior art does describe a number of efforts to make self-inflating structures, such as mattresses and cushions, nevertheless, when those structures are inflated they tend to have a generally convex shape because the exterior fabric layer does not satisfactorily adhere to the entire foam core. In contrast, Applicant's invention completely adheres to the surface of the foam core thereby permitting larger structures, having a defined shape, and which includes concave and compound portions, flat sides and right angle edges.